So I deleted it and everything looks like it's back to normal. The script doesn't append to my markup, either. I am skeptical that simply erasing those lines fixed the entire problem but don't know how to check. Any ideas?

Questions on WordPress Development Stack Exchange are expected to relate to WordPress within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here.
If this question can be reworded to fit the rules in the help center, please edit the question.

I have the same issues on 10 different sites that all got hit today (not all wordpress) and were comprised with the same code. My best guess at this point is that I have malware on my LOCAL machine that used my FTP client to infect my sites.

My bad for storing passwords in the FTP client. I learned from this one.